Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Q25: Focus Session: Thermoelectrics: Controlling Spin |
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Sponsoring Units: GERA DMP FIAP Chair: Joseph Heremans, Ohio State University Room: 503 |
Wednesday, March 5, 2014 2:30PM - 3:06PM |
Q25.00001: Electronic Correlations and Thermoelectric Performance Invited Speaker: Brian Sales Most of the recent progress in improving thermoelectric performance has been due to a reduction of the lattice thermal conductivity. In current state of the art thermoelectric materials the lattice thermal conductivity is near its minimum value, and further improvement in ZT is likely to come from improving the power factor, which depends on the electronic structure. This presentation will discuss the possibility of using electronic correlations to enhance ZT. This work is supported by the Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. [Preview Abstract] |
Wednesday, March 5, 2014 3:06PM - 3:18PM |
Q25.00002: Negative magnetoresistance and s-f scattering in Pb$_{1-x}$Eu$_{x}$Se Sunphil Kim, Yibin Gao, Bin He, Gloria Lehr, Yeseul Lee, Mercouri Kanatzidis, Donald Morelli, Joseph P. Heremans PbSe is cost effective over PbTe and has been a good potential p-type thermoelectric material, showing zT $>$1.\footnote{Yeseul Lee et al., J. Am. Chem. Soc. 135, 2013, 5152-5160.} Also, addition of Eu increases the band gap.\footnote{Arnim Lambrecht et al., J. Cryst. Growth 108, 1991, 301-308.} The valence band of Pb$_{1-x}$Eu$_{x}$Se appears theoretically favorable generating degeneracy between L-points and $\Sigma$-points. Here, we synthesize and characterize p-type doped Pb$_{1-x}$Eu$_{x}$Se:Na using combination of co-melting and Spark Plasma Sintering methods. Thermoelectric, thermomagnetic, and galvanomagnetic properties (electrical resistivity, Seebeck, and Hall) are measured and reported, along with Magnetization and Magnetoresistance. We found out that magnetic scattering is dominant in Pb$_{1-x}$Eu$_{x}$Se, showing negative magnetoresistance. [Preview Abstract] |
Wednesday, March 5, 2014 3:18PM - 3:30PM |
Q25.00003: Intermediate Valence Tuning and Seebeck Coefficient Optimization in Yb-based Low-Temperature Thermoelectric Materials Gloria Lehr, Donald Morelli, Hyungyu Jin, Joseph Heremans Several Yb-based intermediate valence compounds have unique thermoelectric properties at low temperatures. These materials are interesting to study for niche applications such as cryogenic Peltier cooling of infrared sensors on satellites. Elements of different sizes, which form isostructural compounds, are used to form solid solutions creating a chemical pressure (smaller atoms -- Sc) or relaxation (larger atoms -- La) to alter the volume of the unit cell and thereby manipulate the average Yb valence. Magnetic susceptibility measurements show a strong correlation between the Seebeck coefficient and the ratio of trivalent to divalent Yb in these compounds. Two different Yb-based solid solution systems, Yb$_{\mathrm{1-x}}$Sc$_{\mathrm{x}}$Al$_{2}$ and Yb$_{\mathrm{1-x}}$La$_{\mathrm{x}}$Cu$_{\mathrm{2}}$Si$_{2}$, demonstrate that the concentration of Yb can be used to tune both the magnitude of the Seebeck coefficient as well as the temperature at which its absolute maximum occurs. [Preview Abstract] |
Wednesday, March 5, 2014 3:30PM - 3:42PM |
Q25.00004: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 3:42PM - 3:54PM |
Q25.00005: Thermomagnetic properties of single-crystal Holmium Sarah J. Watzman, Yibin Gao, Stephen R. Boona, Joseph P. Heremans This talk will present results of experiments intended to experimentally map out the complete thermomagnetic transport tensor of elemental holmium. An emphasis has been placed on examining the evolution of these properties as the material crosses between its various magnetic phases, including the unusual helical anti-ferromagnetic state. This state is particularly interesting due to the gradual rotation of the local magnetic moments that leads to their net global cancellation, as the impact of this type of ordering on the thermomagnetic transport properties has yet to be fully explored. Specifically, we will report results of the magneto-thermopower, magneto-thermal conductivity, and the Nernst coefficient on single crystal samples. [Preview Abstract] |
Wednesday, March 5, 2014 3:54PM - 4:06PM |
Q25.00006: Phonon induced magnetism in ionic materials Oscar D. Restrepo, Nikolas Antolin, Hyungyu Jin, Joseph P. Heremans, Wolfgang Windl Thermoelectric phenomena in magnetic materials create exciting possibilities in future spin caloritronic devices by manipulating spin information using heat. An accurate understanding of the spin-lattice interactions, i.e. the coupling between magnetic excitations (magnons) and lattice vibrations (phonons), holds the key to unraveling their underlying physics. We report ab initio frozen-phonon calculations of CsI that result in non-zero magnetization when the degeneracy between spin-up and spin-down electronic density of states is lifted for certain phonon displacement patterns. For those, the magnetization as a function of atomic displacement shows a sharp resonance due to the electronic states on the displaced Cs atoms, while the electrons on indium form a continuous background magnetization. We relate this resonance to the generation of a two-level system in the spin-polarized Cs partial density of states as a function of displacement, which we propose to be described by a simple resonant-susceptibility model. Current work extends these investigations to semiconductors such as InSb. ODR and WW are supported by the Center for Emergent Materials, an NSF MRSEC at OSU (Grant DMR-0820414).HJ and JPH are supported by AFOSR MURI Cryogenic Peltier Cooling, Contract \#FA9550-10-1-0533. [Preview Abstract] |
Wednesday, March 5, 2014 4:06PM - 4:18PM |
Q25.00007: Observation of a magnetic field dependence of the lattice thermal conductivity Hyungyu Jin, Oscar Restrepo, Nikolas Antolin, Wolfgang Windl, Stewart Barnes, Joseph Heremans Can phonons respond to magnetic fields? From the simple point of view of the classical lattice vibrations, there is no clue that phonons possess any magnetic characteristics. Here, we report for the first time that the lattice thermal conductivity can show a response to an external magnetic field in a non-magnetic semiconductor crystal. We observe a magnetic field dependence of the lattice thermal conductivity in a high quality 2x10$^{15}$ Te doped single crystal of InSb. The electronic contribution is over 10$^{6}$ times smaller than the lattice. The effect is observed in the temperature regime where the Umklapp processes start appearing, and still mainly involve phonons with long mean free paths. A special thermal design is employed to obtain a high accuracy heat flux measurement. Detailed experimental procedures and results are presented along with a brief discussion about possible origins of the effect. [Preview Abstract] |
Wednesday, March 5, 2014 4:18PM - 4:30PM |
Q25.00008: A possible origin for the colossally large Seebeck coefficient in FeSb$_{2}$ Hidefumi Takahashi, Ryuji Okazaki, Ichiro Terasaki, Yukio Yasui Narrow-gap semiconductor FeSb$_{2}$ has attracted interest because of the recent observation of a colossal Seebeck coefficient $S\simeq -45$ mV/K at 10 K.[A. Bentien $et$ $al$., EPL 80, 17008 (2007).] This compound has a small energy gap $\Delta \sim 5$ meV and $\mid S\mid $ rapidly increases below 40 K, suggesting that $\Delta$ is formed by an unusual mechanism such as a strong electron correlation. However, the reported maximum values of $S$ are remarkably different from sample to sample, ranging from $-500$ $\mu$V/K to $-45$ mV/K. We report a systematic study of ppm-level impurity effects of magnetic and transport properties with single crystals.[H. Takahashi $et$ $al$., JPSJ. 80, 054708 (2011).] A purest sample has a small carrier concentration ($<10^{16}$ cm$^{-3}$ below 30 K) and a large $S$ ($-1400$ $\mu$V/K at 20 K), indicating that the large $S$ predominantly comes from the small carrier density. Moreover, we have measured the magnetic field dependence of transport properties of the purest crystal to investigate the relation between the electronic states and transport properties. We successfully explain the results in terms of an extrinsic semiconductor with ppm-level impurities, suggesting that the large $S$ arises from the low carrier concentration with a phonon-drag [Preview Abstract] |
Wednesday, March 5, 2014 4:30PM - 4:42PM |
Q25.00009: On the thermal Hall effect in the electrically insulating ferrimagnet yttrium iron garnet Stephen R. Boona, Joseph P. Heremans This talk will present results from our recent experiments aimed at measuring the elements of the magneto-thermal conductivity tensor $\kappa _{\mathrm{ijk}}$ of the electrically insulating ferrimagnet yttrium iron garnet (YIG). We will report evidence of a non-zero contribution from $\kappa_{\mathrm{xyz}}$, which suggests the existence of a thermal Hall effect in this material. We will discuss the ramifications of these results in relation to spin caloritronic experiments, as well as some possible concepts for thermal-to-electrical energy conversion applications based on this phenomenon. [Preview Abstract] |
Wednesday, March 5, 2014 4:42PM - 4:54PM |
Q25.00010: Studies on magnetoresistance and magneto-thermopower of single cobalt nanowire D. Kim, J. Kally, M.H.W Chan, N. Samarth, D. Tadigadapa We have studied the magnetoresistance and magneto-thermopower of suspended individual cobalt nanowire using microfabricated thermoelectric workbench. The workbench has embedded heater and thermocouple to provide a temperature gradient along a nanowire and measure temperature of both ends of nanowire. The cobalt nanowire was synthesized by direct electrodeposition and dispersed in solution. It was confirmed that the nanowire is single crystal with hexagonal close-packed structure by TEM analysis. Cobalt nanowires with 70-nm-diameter nanowires were drop-cast on the device and focused-ion-beam-induced deposition of platinum was used to provide mechanical anchors and good electrical and thermal contact between nanowire and the workbench. The magnetic field was applied perpendicular and parallel to wire axis. The absolute value of thermopower increased with perpendicular magnetic field and the value in the saturation state was 0.9 {\%} higher A negative magnetoresistance was observed with 1.3 {\%} smaller resistance in the saturation state. Because of increasing thermopower and decreasing resistance thermoelectric power factor was improved with magnetic field [Preview Abstract] |
Wednesday, March 5, 2014 4:54PM - 5:06PM |
Q25.00011: Spin-Seebeck effect due to thermally driven spin-polarized electron transport on the surface of a three-dimensional topological insulator Po-Hao Chang, Farzad Mahfouzi, Naoto Nagaosa, Branislav Nikolic We study the spin Seebeck effect on the surface of a three-dimensional topological insulator (TI), such as Bi$_2$Se$_3$, in a geometry in which temperature bias is applied parallel to the surface. This generates spin-polarized charge current with polarization component $P_x \simeq 60\%$ along the direction of transport due to surface spin-orbit coupling. The spin current injected from the surface into a third nonmagnetic voltage probe, covering portion of the TI surface across its width, is converted via the inverse spin Hall effect (ISHE) into the voltage signal yielding the spin-Seebeck coefficient \mbox{$|S_{xy}|^{\mathrm{max}} \simeq 30$ nV/K} (assuming the SH angle of Pt voltage probe). Our prediction relies crucially on specific orientation of quintuple layers of Bi$_2$Se$_3$ with respect to the TI surface and direction of transport, as well as on the corresponding proper coupling of electronic spin states with support on the Bi and Se sublattice to spins emitted or absorbed by the three attached normal metal leads. [Preview Abstract] |
Wednesday, March 5, 2014 5:06PM - 5:18PM |
Q25.00012: Thermoelectric corrections to quantum voltage measurement Charles Stafford, Justin Bergfield The voltage measured by a floating probe of a nonequilibrium quantum system is shown to exhibit nontrivial thermoelectric corrections at finite temperature. The voltage probe is modelled as a scanning potentiometer/thermometer that is allowed to equilibrate with a quantum system via local tunnel coupling. Once equilibrated, the net electrical and heat currents flowing into the probe are zero. This generalizes Buettiker's theory of voltage measurement [1] at zero temperature to finite-temperature systems. In a quantum conductor with electrical bias, it is shown that the probe temperature generally differs from ambient temperature due to Peltier cooling/heating within the system, and that the temperature difference can be sizeable for modest bias voltages. Conversely, if the probe is held at ambient temperature, its voltage is shifted from the equilibrated value, leading to a significant error in voltage measurement. However, if there is a large thermal coupling of the probe to the ambient environment, thermal coupling between the probe and system becomes unimportant, and the voltage measurement becomes similar to the process at zero temperature, with negligible thermoelectric corrections. [1] M. Buttiker, Phys. Rev. B 40, 3409 (1989). [Preview Abstract] |
Wednesday, March 5, 2014 5:18PM - 5:30PM |
Q25.00013: Galvanomagnetic and Thermoelectric Properties of Bi$_{2}$Se$_{3-x}$S$_{x}$ Prepared by Spark Plasma Sintering and Annealing Bin He, Yi-Bin Gao, Joseph P. Heremans Bi$_{2}$Se$_{3}$ belongs to the tetradymite class of semiconductors, many of which are known thermoelectric materials. Bi$_{2}$Se$_{3}$ has intrinsic Se vacancies that tend to make it n-type, and the conduction band density of states (DOS) is too low to give a high ZT. Here sulfur is added to pure Bi$_{2}$Se$_{3}$ in order to increase the DOS and reduce vacancy concentration. A group of Bi$_{2}$Se$_{3-x}$S$_{x}$ samples are prepared by SPS, with x varying from 0\% to 10\%. The samples are cut into halves, with one half measured directly and the other annealed before measurement. Thermoelectric properties are measured from 80K to 420K. The Seebeck coefficient increases after annealing while the Hall measurements show the carrier concentration to drop from about 10$^{19}$/cm$^{3}$ to about 10$^{18}$/cm$^{3}$. The DOS increases a little with x, as expected, and the best power factor reached is about 16 $\mu$W/cmK$^{2}$. While the electron concentration can thus be controlled, further work is needed to increase the conduction band DOS more. [Preview Abstract] |
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